Indane bisphenols of formula (I) below and methods for their preparation have been known for some time. Such compounds are useful in the synthesis of many polymers. For example, high molecular weight homo- and copolycarbonates comprising substituted and unsubstituted indane bisphenol monomers are disclosed and claimed in commonly owned U.S. Pat. No. 5,703,197 and copending and commonly owned application Ser. No. 08/947,980 filed Oct. 9, 1997. Such indane polycarbonates are shown to possess unique and advantageous properties. In addition, U.S. Pat. No. 3,634,089 to Hamb discloses the preparation of high molecular weight indane polyesters. Patel et al. describe poly(arylindane)ethers in U.S. Pat. No. 5,145,926, and Paul et al. disclose in U.S. Pat. No. 4,988.785 bismaleimide resins based on indane bisphenols.
Indane bisphenols, as described herein, are represented by the structural formula ##STR1## wherein each R.sup.1 is independently hydrogen, deuterium, halogen, alkyl having 1 to 4 carbons, alkoxy having 1 to 4 carbons, or a deuterated equivalent thereof; each R.sup.2 is an alkyl group having 1 to 4 carbons or a deuterated equivalent thereof; R.sup.3 is hydrogen or deuterium when R.sup.2 is methyl or its deuterated equivalent; otherwise R.sup.3 is an alkyl group or a deuterated equivalent thereof having one less carbon than that of R.sup.2. As used herein, "alkyl" refers to linear or branched saturated hydrocarbon residues containing 1 to 4 carbons. "Alkoxy" refers to the same residues containing, in addition, an oxygen atom at the point of attachment. "Deuterated equivalents thereof", as used herein, refers to the hydrocarbon moieties listed above for R.sup.1, R.sup.2, and R.sup.3 in which at least one hydrogen is replaced with the deuterium isotope. For example, a deuterated methyl group may be CDH.sub.2, CD.sub.2 H, or CD.sub.3, and a deuterated ethyl may be CH.sub.3 CD.sub.2.
The preparation of indane bisphenols of formula (I), also known as hydroxyphenyl indanols, is disclosed in U.S. Pat. No. 2,754,285 to Petropoulos and U.S. Pat. No. 2,819,249 to Petropoulos et al. via an acid-catalyzed dimerization of a-methyl styrene to form indanes, followed by sulfonation of the indanes, and heating the sulfonated product with potassium hydroxide to yield 5-hydroxy-3-(4-hydroxyphenyl)-1,1,3-trimethylindane, wherein each R.sup.1 and R.sup.3 is hydrogen, and R.sup.2 is methyl in structure (I) above. 5-Hydroxy-3-(4-hydroxyphenyl)-1,1,3-trimethylindane is also referred to herein as "IBP".
U.S. Pat. No. 3,288,864 to Farnham discloses a method of IBP production which comprises treating iso-propenylphenol (IPP) with a Friedel-Crafts catalyst at elevated temperatures. U.S. Pat. No. 4,334,106 to Dai discloses somewhat milder reaction conditions in treating IPP or a mixture of its linear oligomers with a stoichiometric excess of organic acid. U.S. Pat. No. 4,791,234 to Faler et al. describes that a decrease in the amount of organic acid used to catalyze the rearrangement of bisphenol A (also referred to herein as "BPA") to form 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (hereinafter, "SBI") leads to the formation of IBP in concentrations of up to 50% in the reaction mixture.
The reaction conditions were further simplified in Japanese Application No. 05294879 which describes a method of producing IBP by treating BPA with an activated clay prepared by Nippon Kassei Hakudo Co. (K-500) at temperatures between 100.degree.-180.degree. C. However, this method requires a lengthy 3-5 hour reaction time. At the completion of the reaction, IBP is precipitated from toluene yielding crystals having a purity between 57% and 78%. Further purification is possible via recrystallization from an aromatic solvent such as toluene, to obtain IBP having a maximum purity of 96% in a 28% yield.
The present invention provides a method for increasing indane bisphenol purity and yield. High purity indane bisphenols (at least 97% pure) previously unreported and in higher yields (34% theoretical) may now be prepared using the present method. In addition, under certain experimental conditions, the present invention allows the reaction time to be significantly cut to as low as 15 minutes. Using a novel set of mild isolation and purification procedures disclosed herein, substantially pure indane bisphenols having a purity of &gt;99% may also be prepared with the present method. These substantially pure materials can then be converted to high molecular weight indane polymers as set forth in the references above.